Gem FAQS > What Is A Gemstone and About Grading and Classifying Gemstones > Color Gradings
For the sake of this discussion I will talk about colored gemstones and deal with diamond colors separately.
Color is the most important property when discussing the beauty of a gemstone. Color is described as hue, saturation and tone. When light strikes the surface of a gemstone some is reflected and some is absorbed. If no light is absorbed the gemstone is allochromatic or colorless.
Hue is the color, ie. blue or greenish-blue or red. The classic subdivision of the rainbow is red, orange, yellow, green, blue and violet and all gemstone colors can be described by using a combination of these colors.
Tone is lightness or darkness of color and is rated by GIA on a scale ranging from-
0- Colorless
1- Extremely Light
2- Very Light
3- Light
4- Medium Light
5- Medium
6- Medium Dark
7- Dark
8- Very dark
9- Extremely Dark
10- Black
Saturation is a bit more complex quantify in that it is the purity of color. Cool color gemstones often appear darker because they have and underlying color of grey that will make them look dull, while warm colors like orange and red have a brown modifier. Saturation is graded by GIA as;
1- brownish or grayish
2- slightly brownish or grayish
3- very slightly brownish or grayish
4- moderately strong
5- strong
6- vivid
The hue tone and saturation need to properly balanced to make a beautiful gem. Too dark of a sapphire looks black and too light looks washed out.
Last updated on June 14, 2009 by Francis M Lynch